Example io demo
This is a guide to the io demo C example project included in the EMAC OE SDK.
IO is an acronym; it stands for Input Output. It refers to data going in and data coming out. In and out of what you ask? Why your machine of course. In this case your machine is the SOM-150ES carrier board.
Input is data going into your machine. Your machine is receiving data, via a port or header, from an external piece of hardware. Mouses, joysticks, keyboards, electronic rain-guages, digital telescopes, burglar alarms and the internet: these all produce streams of data that your machine can store, process, fold, weave and otherwise react to. What your machine does with the data, specifically, depends what software you've got running.
Output is data coming out of your machine. Your machine is sending data, via a port or header, to an external piece of hardware. It's telling that piece of hardware to do something: store some bytes of data, blink an LED, wiggle a robotic tentacle. What data gets sent depends on what software you've got running.
Combined, that's IO. It's how your machine converses with the outside world and without which it is just a sexy paperweight.
The io demo gives us four nice demonstrations of SOM-150ES carrier board IO. We keep it simple. As you might imagine there are some extremely sophisticated IO technologies out there (USB, Ethernet...) but that's a discussion for another time. Here we're just going to work with a general purpose input output (GPIO) header. It's straightforward stuff. Understanding the principals outlined here will equip you to hold meaningful digital conversations with anything from a toaster to a space shuttle.
Contents
Opening, Building and Uploading the Project Files
1. Open the C/C++ editing perspective.
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2. Open the io demo project files.
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3. Build the io demo project.
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4. Upload the io demo binary to the target machine.
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Usage and Behaviour
Hardware Requirements
To use the io demo program you will need the following hardware.
- A SOM-150ES carrier board (Available from EMAC).
- A compatible SoM for that carrier board (SOM-9260M, SOM-9G20M and SOM-9X25 are all compatible and available from EMAC).
- A scrap of homestyle ribbon cable just long enough to reach from GPIO Port B to GPIO Port C. See [Usage Example. IO Demo] for details.
- An analog signal generator. See [Usage Example. AD Demo] for details.
This is a SOM-150ES carrier board carrying an SoM
File:Som150 with SoM.jpg
Usage for io_demo
Refer to these illustrations in our usage examples.
Usage example illustration A
File:PortABC gpio header and LEDs location.jpg
PortB and PortC GPIO headers detail
Execute io demo from the console. It takes no parameters.
./io_demo
This brings up a menu of demos.
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Demo Menu
A/D Demo - a
Count Demo - c
Input to Output Demo - i
Ring Demo - r
Exit - x
Enter Selection:
Now we can press a,c,i or r to run a demo; or x to exit.
Usage Example. A/D Demo
STUB. NEED AN ANALOG WAVEFORM GENERATOR TO USE THIS
Usage Example. Count Demo
From the demo menu press c.
The system counts from 0 to 255 in binary.
The steps of this process are reflected in the GPIO PortC header pins. As each bit in our 8bit register is set to 1, the corresponding pin in the PortC header momentarily registers 5 volts (easily detected with a multimeter or oscilloscope).
More visibly, the process is also reflected in the strip of 8 LEDs on the board (LD1-LD8). A lit LED indicates a 1 in our 8 bit register and an unlit LED indicates a 0. When the counting process is finished all 8 LEDs are lit.
Usage Example. Input to Output Demo
Refer to the SOM-150ES carrier board surface mount LEDs LD1-LD8 for output.
The board lights all 8 LEDs.
Usage Example. Ring Demo
Refer to the SOM-150ES carrier board surface mount LEDs LD1-LD8 for output.
The board lights the LEDs in numeric sequence, 1-8, then repeats; looping until a key is pressed.
